A lock is a device used on canals and rivers to raise and lower boats between stretches of water of different levels. It has a fixed chamber that can vary in water level. When a boat enters an empty lock, the chamber fills with water from the upper level, raising the boat. When full, the boat exits through the upper gates. For a boat going downstream, the process is reversed - it enters a full lock, which then empties to lower the boat to the lower level. Pound locks, first developed in China, have upper and lower gates that control water levels and allow boats to pass through. They are the most common type of lock used today on canals and rivers worldwide.

1. A lock is a device used for raising and low ering boats, ships and other w atercraft between stretches of water of different levels on river and canal w aterways. The distinguishing
feature of a lock is a fixed chamber in w hich the water levelcan be varied; w hereasin a caisson lock, a boat lift, or on a canalinclined plane, it is the chamber itself (usually then called
a caisson) that rises and falls.
Locks are used to make a river more easily navigable, or to allow a canalto cross land that is not level. Later canals used more and larger locks to allow a more direct route to be
taken.
Since 2016, the largest lock w orldwide is the Kieldrecht Lock in the Port of Antw erp,Belgium.
Pou nd lock
A pound lock on the Keitele–Päijänne Canal at Äänekoskiin Central Finland
A pound lock is a type of lock that is used almost exclusively nowadays on canals and rivers. A pound lockhas a chamber w ith gates at both ends that controlthe level of w ater in the
pound. In contrast, an earlier design w ith a single gate w as knownas a flash lock.
Pound locks w ere first used in medieval China during the Song Dynasty (960–1279 AD), having been pioneered by the Song politician and navalengineer Qiao Weiyue in 984.[1]
They
replaced earlier double slipw aysthat had caused trouble and are mentioned by the Chinese polymath Shen Kuo (1031–1095) in his book Dream Pool Essays (published in
1088),[2]
and fully described in the Chinese historicaltextSong Shi (compiled in 1345):[3]
The distance betw een the tw o locks wasrather more than 50 paces, and the w hole space wascovered w ith a great roof like a shed. The gates w ere'hanging gates'; w hen they were
closed the w ater accumulated like a tide until the required level w as reached, and then w hen the time came it w as allow ed to flow out.
The w ater levelcould differ by 4 feet (1.2 m) or 5 feet (1.5 m) at each lock and in the Grand Canal the level w as raised in this w ay by 138 feet (42 m).[3]
In medieval Europe a sort of pound lock w as built in 1373 at Vreeswijk, Netherlands.[4]
This pound lock serviced many ships at once in a large basin. Yet the first true pound lock w as
built in 1396 at Damme near Bruges, Belgium.[4]
The Italian Bertola da Novate (c. 1410–1475) constructed 18 pound locks on the Naviglio di Bereguardo (part of the Milan canal
systemsponsored by Francesco Sforza) between 1452 and 1458.[5]
Use in river navigation

2. Locks on the Rideau Canal, Entrance Valley, near Parliament Hill, Ottaw a, Canada
When a stretch of river is made navigable, a lock is sometimes required to bypass an obstruction such as a rapid, dam, or mill w eir – because of the change in river levelacross the
obstacle.
In large scale river navigation improvements, w eirs and locks are used together. A w eir willincrease the depth of a shallow stretch, and the required lockw illeither be built in a gap in
the w eir, or at the dow nstreamend of an artificial cut w hich bypasses the weir and perhaps a shallow stretch of riverbelow it. A river improved by these means is often called a
Waterw ayor River Navigation (see example Calder and Hebble Navigation).
Sometimes a river is made entirely non-tidal by constructing a sea lock directly into the estuary.
In more advanced river navigations, more locks are required.
 Where a longer cut bypasses a circuitous stretch of river, the upstreamend of the cut w illoften be protected by a flood lock.
 The longer the cut, the greater the difference in river levelbetw een start and end of the cut, so that a very long cut w ill need additional locks along its length. At this point, the cut
is, in effect, a canal.
Use in canals
Locks of the Panama Canal during construction, 1913.
Early completely artificialcanals, across fairly flat countryside, would get round a small hill or depression by simply detouring (contouring) around it. As engineers became more
ambitious in the types of country they felt they could overcome, locks became essentialto effect the necessarychanges in w aterlevelw ithout detoursthat would be completely
uneconomic both in building costs and journey time. Later still, as construction techniques improved, engineers became more w illing to cut directly through and across obstacles by
constructing long tunnels, cuttings, aqueducts or embankments, or to construct even more technicaldevices such as inclined planes or boat lifts. How ever, locks continued to be built
to supplement these solutions, and are an essentialpart of even the most modern navigable w aterways.
Basic construction and operation

3. A plan and side view of a generic, empty canallock. A lock chamber separated fromthe rest of the canal by an upper pair and a low er pair of mitre gates. The gates in each pair close
against each other at an 18° angle to approximate an arch against the w ater pressure on the "upstream" side of the gates w hen the w ater levelon the "dow nstream" side is low er.
Principle of operation of a pound lock
For a boat
going
upstream:
For a boat going
downstream:
1–2. The boat
enters the
lock.
8–9. The boat
enters the
lock.
3. The lower
gates are
closed.
10. The upper
gates are
closed.
4–5. The lock
is filled
w ith
w ater
from
upstream.
11–12. The lock is
emptied by
draining its
w ater
dow nstream.
6. The 13. The low er

4. upper
gates are
opened.
gates are
opened.
7. The boat
exits the
lock.
14. The boat
exits the
lock.
All pound locks have three elements:
 A w atertight chamber connecting the upper and low er canals, and large enough to enclose one or more boats. The position of the chamber is fixed, but its w ater levelcan vary.
 A gate (often a pair of "pointing" half-gates) at each end of the chamber. A gate is opened to allow a boat to enter or leave the chamber; w hen closed, the gate is w atertight.
 A set of lock gear to empty or fill the chamber as required. This is usually a simple valve (traditionally, a flat panel (paddle) lifted by manually w inding a rackand pinion
mechanism) w hich allow swater to drain into or out of the chamber; larger locks may use pumps.
The principle of operating a lock is simple. For instance, if a boat travelling dow nstreamfinds the lockalready full of w ater:
 The entrance gates are opened and the boat moves in.
 The entrance gates are closed.
 A valve is opened, this low ers the boat by draining w ater fromthe chamber.
 The exit gates are opened and the boat moves out.
If the lock w ere empty, the boat w ould have had to w ait 5 to 10 minutes w hile the lock w as filled. For a boat travelling upstream, the process is reversed; the boat enters the empty
lock, and then the chamber is filled by opening a valve that allow s water to enter the chamber fromthe upper level. The w hole operation w illusually take betw een 10 and 20 minutes,
depending on the size of the lock and w hether the water in the lock w as originally set at the boat's level.
Boaters approaching a lock are usually pleased to meet another boat coming tow ardsthem, because this boat w illhave just exited the lock on their leveland therefore set the lock in
their favour – saving about 5 to 10 minutes. How ever, this is not true for staircase locks, whereit is quicker for boats to go through in convoy.
Operation of a canallock
1–3. Boat enters 'empty' lock

5. 4. Bottom gates are closed, bottom paddles closed, top paddles opened, lock starts to fill
5. Lockis filling w ith w ater, lifting boat to the higher level
Details and terminology
An empty lock chamber
For simplicity, this section describes a basic type of lock, w ith a pair of gates at each end of the chamber and simple rackand pinion paddles raised manually by means of a
detachable w indlass operated by lock-keepers or the boat's shore crew. This type can be found all over the w orld, but the terminology here is that used on the British canals. A
subsequent section explains common variations.
Rise[
The rise is the change in w ater-levelin the lock. The tw o deepest locks on the English canalsystemare Bath deep lock[6][7]
on the Kennet and Avon Canal and Tuel Lane Lockon
the Rochdale Canal, w hich both have a rise of nearly 20 feet (6.1 m). Both locks are amalgamations of tw o separate locks, which were combined when the canals were restored to
accommodate changes in road crossings. The deepest "as-built" locks in England are considered to be Etruria Top Lockon the Trent and Mersey Canal and Somerton Deep Lockon
the Oxford Canal: both have a rise of about 14 ft (4.3 m). Again, sources varyas to w hich is the deepest, and in any case Etruria has been deepened over the years to accommodate
subsidence. A more typicalrise (in England) w ould be 7–12 feet (2.1–3.7 metres) (though even shallow er ones can be encountered). By comparison, the Carrapatelo and Valeira locks
on the Douro river in Portugal, w hich are 279 feet (85 m) long and 39 feet (12 m) w ide, have maximum lifts of 115 feet (35 m) and 108 feet (33 m) respectively.[8]
The
tw o Ardnacrusha locks near Limerickon the Shannon navigation in Ireland have a rise of 100 feet (30 m). The upper chamber rises 60 feet (18 m) and is connected to the low er
chamber by a tunnel, w hich when descending does not become visible until the chamber is nearly empty.[9]
Pound
A pound is the level stretch of w aterbetween two locks (also known as a reach).[10]
On American canals, a pound is called a level.
Chamber
The chamber is the main feature of a lock. It is a w atertight (masonry, brick, steelor concrete) enclosure which can be sealed off from the pounds at both ends by means of gates. The
chamber may be the same size (plus a little manoeuvring room) as the largest vesselfor which the waterwaywasdesigned; sometimes larger, to allow more than one such vesselat a
time to use the lock. The chamber is said to be "full" w hen the w aterlevelis the same as in the upper pound; and "empty" w hen the levelis the same as in the low er pound. (If the lock
has no w ater in it at all, perhaps for maintenance w ork, it might also be said to be empty, but it is more usually described as "drained" or "de-w atered".)
Cill
The cill, also spelled sill, is a narrow horizontalledge protruding a short w ayinto the chamber frombelow the upper gates. Allow ing the rear of the boat to "hang" on the cill is the main
danger one is w arned to guard against w hen descending a lock, and the position of the forward edge of the cillis usually marked on the lock side by a w hite line. The edge of the cill is

6. usually curved, protruding less in the center than at the edges. In some locks, there is a piece of oak about 9 in (23 cm) thick w hich protectsthe solid part of the lock cill. On the Oxford
Canal it is called a Babbie; on the Grand Union Canal it is referred to as the cill Bumper. Some canal operation authorities, primarily in the United States and Canada, call the ledge
a miter sill (mitre sill in Canada).[11]
Photo gallery
The cill exposed in the deep Pont de Flandre lock on the Canal Saint-Denis, Paris

Top gate of a lock, show ing the balance beams and paddle w inding gear

200-year-old paddle gear on the Wiener Neustädter Kanal, Austria

7. 
Water conservation gear on the Birmingham Canal Navigations

Lock gate controls on a canal
Gates
Gates are the w atertight doors which sealoff the chamber fromthe upper and low er pounds. Each end of the chamber is equipped w ith a gate, or pair of half-gates, made
of oak or elm (or now sometimes steel). The most common arrangement, usually called miter gates, w asinvented by Leonardo da Vinci, sometime around the late 15th
century.[12]
When closed, a pair meet at an angle like a chevron pointing upstreamand only a very small differencein w ater-levelis necessary to squeeze the closed gates securely
together. This reduces any leaks from betw een themand prevents their being opened until w ater levels have equalised. If the chamber is not full, the top gate is secure; and if the
chamber is not completely empty, the bottom gate is secure (in normal operation, therefore, the chamber cannot be open at both ends). A low er gate is taller than an upper gate,
because the upper gate only has to be tall enough to close off the upper pound, w hile the low er gate has to be able to seal off a fullchamber. The upper gate is as tall as the canalis
deep, plus a little more for the balance beam, w inding mechanism, etc.; the low er gate's height equals the upper gate plus the lock's rise.
Balance beam
A balance beam is the long arm projecting from the landw ard side of the gate over the tow path. As wellas providing leverage to open and close the heavy gate, the beam also
balances the (non-floating) w eight of the gate in its socket, and so allow s the gate to sw ing more freely.
Paddle
A paddle – sometimes know n as a slacker, clough, or (in American English) wicket – is the simple valve by w hich the lockchamber is filled or emptied. The paddle itself is a sliding
w ooden (or nowadaysplastic) panelw hich when "lifted" (slid up) out of the w ay allow swaterto either enter the chamber from the upper pound or flow out to the low er pound. A gate
paddle simply covers a hole in the low er part of a gate; a more sophisticated ground paddle blocks an underground culvert. There can be up to 8 paddles (tw o gate paddles and tw o
ground paddles at both upper and low er ends of the chamber) but there w illoften be fewer. For a long period since the 1970s it w as British Waterways policy not to provide gate
paddles in replacement top gates if tw o ground paddles existed. The reason for this w asgiven as safety, since it is possible for an ascending boat to be sw amped by the w ater froma
carelessly lifted gate paddle. How ever, without the gate paddles the locks are slow er to operate and this has been blamed in some places for causing congestion. Since the late 1990s
the preferred method has been to retain or re-install the gate paddles and fit 'baffles' across themto minimise the risk of inundation.

8. On the old Erie Canal, there w as a danger of injury w hen operating the paddles: w ater, on reaching a certain position, w ould push the paddles w ith a force which could tear the
w indlass (or handle) out of one's hands, or if one w as standing in the w rong place, could knockone into the canal, leading to injuries and drow nings.[13]
Winding gear or paddle gear
Winding gear is the mechanism w hich allows paddles to be lifted (opened) or low ered (closed). Typically, a square-section stub emerges fromthe housing of the w inding gear. This is
the axle of a sprocket ("pinion") w hich engages with a toothed bar ("rack") attached by rodding to the top of the paddle. A lock-keeper or member of the boat's shore crew engages the
square socket of their w indlass (see below) onto the end of the axle and turns the w indlass perhapsa dozen times. This rotates the pinion and lifts the paddle. A paw lengages with the
rackto prevent the paddle from dropping inadvertently w hile being raised, and to keep it raised w hen the w indlassis removed, so that the operator can attend to other paddles.
Now adays it is considered discourteousand w astefulof waterto leave a paddle open after a boat has left the lock, but in commercial days it w as normalpractice. To low er a paddle
the paw lmust be disengaged and the paddle w ound down with the w indlass. Dropping paddles by knocking the paw loff can cause damage to the mechanism; the paddle gear is
typically made of cast iron and can shatter or crackw hen dropped froma height. In areas w here water-wastage due to vandalism is a problem, (for example the Birmingham Canal
Navigations), paddle mechanisms are commonly fitted w ith vandal-proof locks (nowadaysrebranded "water conservation devices") which require the boater to employ a key before the
paddle can be lifted. The keys are officially know n as "water conservation keys", but boaters usually refer to themas T-keys, fromtheir shape; handcuff keys because the original
locks, fitted on the Leeds and LiverpoolCanal, resembled handcuffs; Leeds and Liverpool Keys after that canal; or simply Anti-Vandal Keys.
Hydraulic paddle gear
During the 1980s, British Waterw ays began to introduce a hydraulic systemfor operating paddles, especially those on bottom gates, w hich are the heaviest to operate. A metal
cylinder about a foot in diameter w as mounted on the balance beam and contained a small oil-operated hydraulic pump. A spindle protruded fromthe front face and w as operated by a
w indlass in the usualw ay, the energy being transferred to the actualpaddle by small bore pipes. The systemw aswidely installed and on some canals it became very common. There
turned out to be tw o serious drawbacks. It w asmuch more expensive to install and maintain than traditional gear and w ent wrong more frequently, especially once vandals learned to
cut the pipes. Even w orse, it had a safety defect, in that the paddle once in the raised position could not be dropped in an emergency, but had to be w ound down, taking a good deal
longer. These factors led to the abandonment of the policy in the late 1990s, but examples of it survive allover the system, as it is usually not removed until the gates need replacing,
w hich happens about every twenty years.
Windlass ("lock key)
Collection of lock w indlasses. Note: rakes are for clearing trash out of the lock.
A windlass (also variously 'lockhandle', 'iron' or simply 'key') is a detachable crankused for opening lock paddles (the w ord does not refer to the w inding mechanismitself).

9. The simplest w indlass is made froman iron rod of circular section, about half an inch in diameter and tw o feet long, bent to make an L-shape w ith legs of slightly different length. The
shorter leg is called the handle, and the longer leg is called the arm. Welded to the end of the arm is a square, sometimes tapered, socket of the correct size to fit onto the spindle
protruding fromlock w inding gear.
 Socket: Traditionally, w indlasseshad a single socket, designed for a particular canal. When undertaking a journey through severalcanals w ith different lock-gear spindle sizes it
w as necessary to carryseveraldifferent windlasses. A modern w indlassusually has two socketsfor use on different canals: the smaller is for the British Waterw aysstandard
spindle, fitted in the early 1990s almost everywhere, the larger for the gear on the Grand Union Canal north of Napton Junction, w hich they were unable/unwilling to convert.
 Handle: The handle is long enough for a tw o-handed grip and is far enough fromthe socket to give enough leverage to w ind the paddle up or dow n. There may be a freely
rotating sleeve around the handle to protect the hands fromthe friction of rough iron against skin.
 Arm: A "long throw "windlasshas a longer arm so that the handle is further fromthe socket to give a greater leverage on stiffer paddles. If the throw is too long then the user,
w inding a gate paddle, risks barking their knuckles against the balance beam w hen the handle is at the low est point of its arc. A sophisticated modern w indlassmay have an
adjustable-length arm.
 Materials : Early w indlasses were individually hand forged froma single piece of w rought iron by a blacksmith. More modern techniques include casting of iron or bronze, drop
forging and (the most common technique) w elding. Some boatmen had their w indlasses 'silvered' (or chrome plated) for increased comfort and to prevent rusting. Windlasses are
now only rarely plated, but a popular modern choice of metal is aluminium, w hose smooth and rustproof surface has the same advantages of longevity and blister-reduction, and
is also very light. One type of these, the Dunton Double, has only a single eye, but by clever tapering it w illoperate either size of spindle.
On the Chesapeake and Ohio Canal, the lockkeepers w ere required to remove the w indlasses fromalllock paddles at night, to prevent unauthorized use.[14]
"Turning" a lock
"Turning" a lock can simply mean emptying a fulllock, or filling an empty one ("We entered the lock, and it only took us five minutes to turn it"). It is used more often to refer to a lock
being filled or emptied for the benefit of someone else ("The lock w asturned for us by a boat coming the other w ay") and sometimes the opposite ("The lock w as set forus, but the
crew of the boat coming the other w ay turned it before w e got there").
Swell or Swelling
A swell w as caused by opening suddenly the paddle valves in the lock gates, or w hen emptying a lock.[15]
To help boats leave (dow nstream) a lock, the locksman w ould sometimes
open the paddles to create a sw ell, w hich would help "flush" the boat out of the lock. In one case, a boatsman asked for a backsw ell, that is, open and shut the paddles a few times to
create some w aves, to help him get off the bank w here he wasstuck.[16]
If boats ran aground (frombeing overloaded) they sometimes asked passing crewsto tell the upstreamlock to
give them an extra heavy swell, w hich consisted of opening all the paddles on the lock gate, creating a surge that affected the w hole pound below.[17]
On the Erie Canal, some loaded boats needed a sw ellto get out of the lock, particularly lumber boats, being top heavy, w ould list to one side and get stuckin the lock, and needed a
sw ellto get them out. Some lockkeepers w ould give a sw ellto anyone to help them on the w ay, but some w ould askfor money for the sw ell.[15]
The Erie Canal management did not like sw elling for two reasons. First, it used too much w ater lowering the water on the pound above sometimes causing boats to run aground. In
addition, it raised the w ater levelon the pound below causing some boats to strike bridges or get stuck.[15]
"Lock mooring
"Lockmooring" w as a commonly used method of navigating into a lock by a barge travelling upstream. The barge w ould be directed to the slackw ater to one side of the lock gates and
as the volume of w ater decreased as the lockemptied the barge or boat is effectivelysucked out of the slackw ater into the path of the lock gates. The effort required to navigate the
barge or boat into the mouth of the lock w as therefore substantially reduced.
Snubbing posts

10. Snubbing a boat to keep it fromhitting the dow nstreamgates. Note the rope w rapped around the snubbing post.
On horse-drawn and mule-drawn canals, snubbing posts were used to slow or stop a boat in the lock. A 200-ton boat moving at a few miles an hour could destroy the lock gate. To
prevent this, a rope w as wound around the snubbing post as the boat entered the lock. Pulling on the rope slow ed the boat, due to the friction of the rope against the post.[18]
A rope
2½ inches (6.3 cm) in diameter and about 60 feet (18 meters) long w as typically used on the Erie Canal to snub a boat in a lock.[19]
One incident, w hich tookplace in June 1873 on the Chesapeake and Ohio Canal, involved the boat the HenryC. Flagg and its drunk captain. That boat w as already leaking; the crew ,
having partially pumped the w ater out, entered Lock74, moving in front of another boat. Because they failed to snub the boat, it crashed into and knocked out the dow nstreamgates.
The outrush of w ater fromthe lock caused the upstream gates to slam shut, breaking them also, and sending a cascade of water over the boat, sinking it. This suspended navigation
on the canalfor 48 hours until the lock gates could be replaced and the boat removed from the lock.[20]
Variations
A series of photos of the Canadian Locks in Sault Ste. Marie to illustrate a drop of about 22 ft (6.7 m) in a lock.
Variations exist for types of locks and the terminology used for them.
 Single gates on narrow canals (locks approx. 7 feet or 2.1 metres w ide)
 On most English narrow canals, the upper end of the chamber is closed by a single gate the fullw idth of the lock. This w as cheaperto construct and is quicker to operate
w ith a small crew, as only one gate needs to be opened. These w ere often fitted with a post allow ing a rope to be used to stop the boat and close the gate at the same time.

11.  Some narrow locks (e.g. on Birmingham Canal Navigations) go even further. They have single gates at the low er end also. This speeds up passage, even though single
low er gates are heavy (heavier than a single upper gate, because the low er gate is taller) and the lockhas to be longer (a low er gate opens INTO the lock, it has to pass the
bow or stern of an enclosed boat, and a single gate has a w ider arc than tw o half-gates).
 A few narrow locks imitate w ide locks in having paired gates at both ends. An example is the Bosley LockFlight on the Macclesfield Canal.
 Steel gates. Steel gates and/or balance beams are frequently used nowadays, although all-wooden versions are stillfitted w here appropriate.
 Sw inging gates. Even very large steel-gated locks still can use essentially the same sw inging gate design as small 250-year-old locks on the English canals. On English
canals, steelgates usually have w ooden mitre posts as this gives a better seal.
 Sliding gates. Some low -head locks use sliding steelgates (see Kiel Canal). The sliding gates of the Nieuw e Meersluis in Amsterdam double as roadw ays.
 Caisson gates. A kind of sliding gate that is hollow and can float. It can be constructed to withstand high heads.
 Guillotine gates. Some locks have vertically moving steelgates – these are quite common on river navigations in East Anglia. Sometimes just one of the pairs of sw inging
gates is replaced by a guillotine: for instance at Salterhebble Locks, w here space to swing the balance beams of bottom gates of the low est lockw asrestricted by bridge
w idening. On the River Nene most locks have this arrangement as in time of flood the top mitre gates are chained open and the bottom guillotines lifted so that the lock
chamber acts as an overflow sluice. Guillotine gates are also used on the dow nstreamside of larger locks such as the 23m Bollène lock on the River Rhône, the aperture
being large enough for a boat to travelunder it.
 Vertically rotating gates (American usage: Drop gates)
Example of a lock w ith a drop gate (Lock10) on the Chesapeake and Ohio Canal
are gates w hich, when open, lie flat on the canal bed and w hich close by lifting (London Flood Barrier). Some of these w ere installed on the Chesapeake and Ohio Canal in
the congested 7 Locks area since they could be operated by one man and also could speed up traffic.
 Rotating-sector gates. Some of these w orkvery like traditional sw inging gates, but w ith each gate in the formof a sector of a cylinder. They close by rotating out fromthe
lock w alland meeting in the centre of the chamber. Water is let in or out by opening the gates slightly: there are no paddles or other lock gear. The lock at Limehouse Basin,
w hich gives accessto the River Thames, is an example. A dramatically large one can be seen at the Maeslantkering (huge flood gates) near Rotterdam. There is a different
type at the sea lock on the Ribble Link: this is a rising sector gate, w hich has a horizontalaxis: the gate drops to the bed of the river to allow boats to pass.
 Different paddle gear
 Some manually operated paddles do not require a detachable handle (w indlass) because they have their handles ready-attached.

12.  On the Leeds and LiverpoolCanal there is a variety of different lockgear. Some paddles are raised by turning w hat is in effect a large horizontalw ing nut (butterflynut)
lifting a screw-threaded bar attached to the top of the paddle. Others are operated by lifting a long w ooden lever, which operates a wooden plate which seals the culvert.
These are know n locally as "jackcloughs". Bottom gate paddles are sometimes operated by a horizontalratchet w hich also slides a w ooden plate sideways, rather than the
more common verticallift. Many of these idiosyncratic paddles have been "modernised" and they are becoming rare.
 On the Calder and Hebble Navigation, some paddle gear is operated by repeatedly inserting a Calder and Hebble Handspike (length of 4" by 2" hardw ood)into a ground-
level slotted w heeland pushing dow n on the handspike to rotate the w heelon its horizontalaxis.
 On some parts of the Montgomery Canal bottom paddles are used in place of side paddles. Rather than passing into the lock through a culvert around the side of the lock
gate, the w ater flowsthrough a culvert in the bottom of the canal. The paddle slides horizontally over the culvert.
 Composite locks. To economise, especially w here good stone w ould be prohibitively expensive or difficult to obtain, composite locks w ere made, i.e. they w ere constructed using
rubble or inferior stone, dressing the inside w alls of the lockw ith w ood, so as not to abrade the boats. This w as done, for instance, on the Chesapeake and Ohio Canal w ith the
locks near the Paw Paw Tunnel[21]
and also the Chenango Canal[22]
Because the w ood would swell(making the lock space smaller) or rot aw ay, the wood was often replaced by
concrete.
 Lock keepers.
Some locks are operated (or at least supervised) by professionalor volunteer lockkeepers. This is particularly true on commercial w aterways, or where locks are large or have
complicated features that the average leisure boater may not be able to operate successfully. For instance, although the Thames above Teddington (England) is almost entirely a
leisure w aterway, the locks are usually staffed. Only recently have boaters been allow ed limited access to the hydraulic gear to operate the locks w hen the keeper is not present.
 Pow ered operation. On large modern canals, especially very large ones such as ship canals, the gates and paddles are too large to be hand operated, and are operated
by hydraulic or electrical equipment. On the Caledonian Canal the lock gates w ere operated by man-powered capstans, one connected by chains to open the gate and another to
draw it closed. By 1968 these had been replaced by hydraulic pow er acting through steelrams.[23]
Even on smaller canals, some gates and paddles are electrically operated,
particularly if the lock is regularly staffed by professionallockkeepers. On the River Thames below Oxford allthe locks are staffed and powered. Poweredlocks are usually still
filled by gravity, though some very large locks use pumps to speed things up.
 Fish Ladders. The construction of locks (or weirs and dams) on rivers obstructsthe passage of fish. Some fish such as lampreys, trout and salmon go upstreamto spaw n.
Measures such as a fish ladder are often taken to counteract this. Navigation locks have also potential to be operated as fishways to provide increased accessfor a range of
biota.[24]
 Weigh lock.
A w eigh lockon the Lehigh canal
A w eigh lockis a specialized canal lock designed to determine the w eight of barges to assesstollpayments based upon the w eight and value of the cargo carried. The Erie Canal had
a w eigh locks in Rochester, Syracuse, and West Troy New York. The Lehigh Canal also had w eigh locks (see photo on right).
Special cases

13. Lock flights
The flight of 16 locks at Caen Hill on the Kennet and Avon Canal
Loosely, a flight of locks is simply a series of locks in close-enough proximity to be identified as a single group. For many reasons, a flight of locks is preferable to the same number of
locks spread more w idely: crews are put ashore and picked up once, rather than multiple times; transition involves a concentrated burst of effort, ratherthan a continually interrupted
journey; a lock keeper may be stationed to help crewsthrough the flight quickly; and w here wateris in short supply, a single pump can recycle w ater to the top of the w hole flight. The
need for a flight may be determined purely by the lie of the land, but it is possible to group locks purposely into flights by using cuttings or embankments to "postpone" the height
change. Examples: Caen Hill locks, Devizes.
"Flight" is not synonymous w ith "Staircase" (see below). A set of locks is only a staircase if successive lockchambers share a gate (i.e. do not have separate top and bottom gates w ith
a pound betw een them). Most flights are not staircases, because each chamber is a separate lock(w ith its ow n upper and low ergates), there is a navigable pound (how evershort)
betw een each pair of locks, and the locks are operated in the conventionalw ay.
How ever, some flights include (or consist entirely of) staircases. On the Grand Union (Leicester) Canal, the Watford flight consists of a four-chamber staircase and three separate
locks; and the Foxton flight consists entirely of two adjacent 5-chamber staircases.
Staircase locks
Staircase of five locks, dating from1774, at Bingley, England
Where a very steep gradient has to be climbed, a lockstaircase is used. There are tw o types of staircase, "real" and "apparent".
A "real" staircase can be thought of as a "compressed" flight, w here the intermediate pounds have disappeared, and the upper gate of one lock is also the low er gate of the one above
it. How ever, it is incorrect to use the terms staircase and flight interchangeably: because of the absence of intermediate pounds, operating a staircase is very different fromoperating a

14. flight. It can be more usefulto think of a staircase as a single lock w ith intermediate levels (the top gate is a normal top gate, and the intermediate gates are all as tall as the bottom
gate). As there is no intermediate pound, a chamber can only be filled by emptying the one above, or emptied by filling the one below : thus the w hole staircase has to be full of w ater
(except for the bottom chamber) before a boat starts to ascend, or empty (except for the top chamber) before a boat starts to descend. By building a pair of such locksets (one used to
climb and the other to descend) these difficulties are avoided, as w ellas enabling a greater traffic volume and reduced w ait times.
In an "apparent" staircase the chambers stillhave common gates, but the w ater does not pass directly fromone chamber to the next, going instead via side ponds. This means it is not
necessary to ensure that the flight is fullor empty before starting.
Examples of famous "real" staircases in England are Bingley and Grindley Brook. Tw o-rise staircasesare more common: Snakeholme Lockand Struncheon Hill Lock on the Driffield
Navigation w ere converted to staircase locks afterlow water levels hindered navigation over the bottom cill at all but the higher tides – the new bottomchamber rises just far enough to
get the boat over the original lock cill. In China, the recently completed Three Gorges Dam includes a double five-step staircase forlarge ships, and a ship lift for vessels of less than
3000 metric tons. Examples of "apparent" staircasesare Foxton Locks and Watford Locks on the Leicester Branch of the Grand Union.
Instructions for descent of treble staircase,Chesterfield Canal
Operation of a staircase is more involved than a flight. Inexperienced boaters may find operating staircase locks difficult. The key w orries(apart fromsimply being paralysed w ith
indecision) are either sending dow n more w ater than the low er chambers can cope with (flooding the tow path, or sending a w ave along the canal) or completely emptying an
intermediate chamber (although this show sthat a staircase lockcan be used as an emergency dry dock). To avoid these mishaps, it is usual to have the w hole staircaseempty before
starting to descend, or fullbefore starting to ascend, apart fromthe initial chamber.
One striking difference in using a staircase of either type (compared w ith a single lock, or a flight) is the best sequence for letting boats through. In a single lock (or a flight w ith roomfor
boats to pass) boats should ideally alternate in direction. In a staircase, however, it is quicker for a boat to follow a previous one going in the same direction. Partly for this reason
staircase locks such as Grindley Brook, Foxton, Watford and Bratch are supervised by lockkeepers, at least during the main cruising season, they normally try to alternate as many
boats up, follow ed by down as there are chambers in the flight.
As w ith a flight, it is possible on a broad canalfor more than one boat to be in a staircase at the same time, but managing this w ithout wasteof water requires expertise. On English
canals, a staircase of more than tw o chambers is usually staffed:the lockkeepers at Bingley (looking after both the "5-rise" and the "3-rise") ensure that there are no untow ard events
and that boats are moved through as speedily and efficiently as possible. Such expertise permits miracles of boat balletics: boats travelling in opposite directions can pass each other
halfw ayup the staircase by moving sidew aysaround each other; or at peak times, one can have all the chambers fullsimultaneously w ith boats travelling in the same direction.
Doubled, paired or twinned locks[edit]

15. Doubled locks. Left lock has boat in it, right lock (center of drawing) is empty. This is on the Erie Canal at Lockport
Locks can be built side by side on the same w aterway. This is variously called doubling, pairing, or twinning. The Panama Canal has three sets of double locks. Doubling gives
advantages in speed, avoiding hold-ups at busy times and increasing the chance of a boat finding a lock set in its favour. There can also be w ater savings: the locks may be of
different sizes, so that a small boat does not need to empty a large lock; or each lock may be able to act as a side pond (w ater-saving basin) for the other. In this latter case, the w ord
used is usually "tw inned": here indicating the possibility of saving w aterby synchronising the operation of the chambers so that some w ater fromthe emptying chamber helps to fill the
other. This facility has long been w ithdrawn on the English canals, although the disused paddle gear can sometimes be seen, as at Hillmorton on the Oxford Canal. Elsew here they are
still in use; a pair of tw inned locks has been opened in 2014 on the Dortmund-Ems Canal near Münster, Germany.[25]
The once-famous staircase at Lockport, New York was also a doubled set of locks. Five tw inned locks allow ed east- and w est-bound boats to climb or descend the 60 feet
(18 m) Niagara Escarpment, a considerable engineering feat in the nineteenth century. While Lockport today has tw o large steellocks, half of the old tw in stair acts as an emergency
spillw ay and can still be seen, w ith the original lock gates having been restored in early 2016.[26]
These terms can also (in different places or to different people) mean either a tw o-chamber staircase (e.g. Turner Wood Double Locks on the Chesterfield Canal: the same canal has a
three-rise staircase called Thorpe Low Treble locks), or just a flight of tw o locks (as at Thornhill Double Locks on the Calder and Hebble Navigation). Also, "double lock" (less often,
"tw in lock") is often used by novices on the English canals to mean a w ide (14 ft) lock, presumably because it is "double" the w idth of a narrow lock, and allow s two narrow boats going
in the same direction to "double up". These are properly know n as broad locks.
Stop locks

16. Lifford lane guillotine lock, Kings Norton, Birminghambetw een the Stratford-upon-Avon Canaland the Worcester and Birmingham Canal
A "stop" lock is a (very) low -rise lockbuilt at the junction of tw o (rival) canals to prevent water frompassing between them.
During the competitive years of the English w aterwayssystem, an established canalcompany w ould often refuse to allow a connection froma new er, adjacent one. This situation
created the Worcester Bar in Birmingham, w here goods had to be transshipped betw een boats on rivalcanals only feet apart.
Where a junction w as built, either because the older canalcompany saw an advantage in a connection, or w here the new company managed to insert a mandatory connection into its
Act of Parliament, then the old company w ould seekto protect (and even enhance) its w ater supply. Normally, they w ould specify that, at the junction, the new er canalmust be at a
higher level than their existing canal. Even though the drop fromthe new er to the older canal might only be a few inches, the difference in levels stillrequired a lock – called a stop
lock, because it w asto stop w ater flowing continuously between the new ercanaland the older, low er one. The lock w ould be under the controlof the new company, and the gates
w ould, of course, "point" uphill - tow ardsthe newer canal. This w ould protect the water supply of the new ercanal, but w ould nevertheless"donate" a lockfulof water to the older
company every time a boat w ent through. In times of excess water, of course, the lock"bywash"would continuously supplywaterto the low er canal.
When variable conditions meant that a higher w ater levelin the new canalcould not be guaranteed, then the older company w ould also build a stop lock(under its ow n control, with
gates pointing tow ards its own canal) which could be closed w hen the new canalwas low. This resulted in a sequentialpair of locks, w ith gates pointing in opposite directions: one
example w as at Hall Green near Kidsgrove, w here the southern terminus of the Macclesfield Canal joined the Hall Green Branch of the earlier Trent and Mersey Canal. The four gate
stop lock near Kings Norton Junction, betw een the Stratford-upon-Avon Canaland the Worcester and Birmingham Canal w as replaced in 1914 by a pair of guillotine lock gates w hich
stopped the w ater flow regardless of which canalwashigher. These gates have been permanently open since nationalisation.[27]
Many stop locks w ere removed or converted to a single gate after nationalisation in 1948. Hall Green stop lock remains, but as a single lock: the extra lockw as removed because the
low ering of the T&M's summit pound (to improve Harecastle Tunnel's "air draught" – its free height above the w ater level) meant that the T&M w ould alw aysbe low erthan the
Macclesfield. The Hall Green Branch is now considered to be an extension of the Macclesfield Canal, w hich now meets the T&M at Hardings Wood Junction (just short of the
Harecastle Tunnel north portal).
It should be noted that the new er canalw asnot alw aysat a higher level than the one it joined. For instance, there is a very shallow lockat Autherley Junction, w here the 1835
Birmingham and Liverpoolcanal(now part of the Shropshire Union Canal) met the older Staffordshire and Worcestershire Canal, build in 1772. The Nicholson guide show sthat a
boater travelling south along the new er canallocks "up" before turning north or south onto the older Staffordshire and Worcestershire Canal – so the Shropshire Union Canal gains a
small lockfulof w ater each time a boat passes. How ever, the gain is tiny since the leveldifference is so small that it is sometimes possible to open both gates at once.
Round locks
Agde Round Lock
There are severalexamples w here locks have been built to a round plan, w ith more than tw o exits fromthe lock chamber, each serving a different water level. Thus the lock serves
both as a w ay of changing levels and as a junction. The circular plan of the lock allow s boats w ithin it to rotate to line up w ith the appropriate exit gate.
The best know n example of such a round lock is the Agde Round Lockon the Canal du Midi in France. This serves as a lockon the main line of the canaland allow s accessto
the Hérault River.[28]

17. A second French round lock can be found in the formof the, now disused, Écluse des Lorraines, connecting the Canal latéral à la Loire w ith the River Allier.[29]
Drop locks
Dalmuir drop lock
A drop lock allow s a short length of canalto be low ered temporarily while a boat passes under an obstruction such as a low bridge. During canal restoration, a drop lock may be used
w here it is impractical or prohibitively expensive to remove or raise a structure that w asbuilt after the canalw as closed (and where re-routing the canalis not possible).
A drop lock can consist of two conventionallockchambers leading to a sump pound, or a single long chamber incorporating the sump - although the term properly applies only to the
second case. As the pounds at either end of the structure are at the same height, the lock can only be emptied either by allow ing w aterto run to w aste fromthe sump to a low er stream
or drain, or (less w astefully)by pumping w ater backup to the canal. Particularly in the tw o-chamber type, there w ould be a need for a bypass culvert, to allow water to move along the
interrupted pound and so supply locks further down the canal. In the case of the single-chamber type, this can be achieved by keeping the lock fulland leaving the gates open w hile
not in use.[30]
While the concept has been suggested in a number of cases, the only example in the w orld of a drop lockthat has actually been constructed is at Dalmuir on the Forth and Clyde
Canal in Scotland.[31]
This lock, of the single chamber type, w as incorporated during the restoration of the canal, to allow the replacement of a sw ing bridge (on a busy A road) by a
fixed bridge, and so answ er criticisms that the restoration of the canalw ould cause frequent interruptions of the heavy road traffic. It can be emptied by pumping – but as this uses a lot
of electricity the method used w hen watersupplies are adequate is to drain the lock to a nearby burn. A series of pictures showing the operation of the lockcan be seen here.[32]
Flood locks
A flood lock is to prevent a river fromflooding a connected w aterway. It is typically installed w here a canalleaves a river. At normal river levels, the lock gates are left open, and the
height of the canalis allow ed to rise and fallw ith the height of the river.
How ever, if the river floods beyond a safe limit for the canal, then the gates are closed (and an extra lock created) untilthe river drops again. Since this is a true lock it is possible for
boats to leave the canal for the flooded river despite the difference in w ater levels (though this is not likely to be w ise) or (more sensibly) to allow boats caught out on the flood to gain
refuge in the canal.
Note that if the canal is simply a navigation cut connecting tw o stretchesof the same river, the flood lock w illbe at the upstream end of the cut (the dow nstreamend w illhave a
conventionallock).
Flood locks w hich have been used only as flood gates (see below ) are often incapable of reverting to their former purpose w ithout refurbishment. That is, w here only outer gates are
ever closed (probably because a w aterwayis not a true commercial one, and therefore there is no financial imperative for a boat to venture out onto a flooded river) inner gates soon
suffer fromlackof maintenance. A good example is on the Calder and Hebble Navigation, w here structuresreferred to in the boating guides as "Flood Locks" are clearly only capable
of being used for flood-prevention, not for "penning" boats to or fromthe river in flood.
Flood gates[

18. Bi-directional flood gates on the canal Schoten-Dessel, Belgium
Flood gate or Stop gate (American usage) on Chesapeake and Ohio Canal. When a flood threatened, boards w ere put in the lock to divert w atersfromthe canalto the Potomac river.
Note w inch house on top for the boards.
A flood gate or "stop gate" is the cheaper equivalent of a flood lock. Only one set of gates exist, and so w hen the river is higher than the canal, the gates are closed and navigation
ceases. These are quite common in the French inland w aterwayssystem. Flood gates may also be used to sub-divide long canalpounds or protect, in case of bankcollapse, the
surrounding area if this is low er than the w ater levelof the canal. They are commonly found at the ends of long embankments and at aqueducts. These gates are often overlooked
because they lackbalance beams and are only a little higher than normal canal level.
Bi-directional gates and locks

19. Bi-directional gates at one chamber end of a tidal lock (located in Veurneon the canal Nieuw poort - Duinkerke)
Where a lock is tidal (i.e. one side of the lock has w ater whose levelvaries with the tide) or w here a canalmeets a river w hose levelmay vary, the w ater on the tidal or river side (the
"dow nstream" side) may rise above the w ater on the normal "upper" side. The "upstream" pointing doors w illthen fail to do their job, and w illsimply drift open. To prevent w aterflowing
the w rong way through the lock, there w illneed to be at least one set of gates pointing in the "w rong"direction. If it is desirable that boats can use the lock in these circumstances, then
there needs to be a full set of gates pointing tow ardsthe tidal or river side. The usualmethod is to have gates pointing in opposite directions at both ends of the chamber (alternatively,
the "paired stop lock" arrangement of tw o separate sequentiallocks pointing in opposite directions w ould w orkhere – but w ould require an extra chamber). If navigation is not required
(or impossible) at one "extreme" (e.g. allow navigation above mid-tide, but just prevent the canalemptying at low tide) then it is only necessary to have one set of bi-directionalgates.
Tw o types of bidirectionallocks at the end of the Marne-Rhine Canal in the Independent Port of Strasbourg
A sea lock is one that connects a canalor river directly w ith an estuary or ocean. Allsea locks are tidal.
Tidal locks
Sea lock at Bude, Cornw all

20. A tidal lock is generally any lock that connects tidal w ith non-tidalw ater. This includes a lock betw een a tidalriver and the non-tidal reaches, or between a tidalriver and a canal, or a
sea lock. How ever, the termusually refers specifically to a lock w hose method of operation is affected by the state of the tide. Examples:
 A canal joining a river whose levels are always lower than the canal. Allthat is needed is an ordinary lock, w ith the gates pointing up the canal. The lockis used normally so long
as the tide is high enough to float boats through the low er gates. If near low tide the lock becomes unusable, then the gates can be barred (and simply become a "reverse flood
gate", holding w ater in the canal). This arrangement also applies to some sea locks (e.g. Bude Canal).
 A canal joining a river which is normallybelowit, but which can rise above it (at very high tides, or after heavy rain). One pair of gates can be made bidirectional, i.e. the inw ard-
pointing gates w ould be supplemented by a pair pointing out to the river. When the river is higher than the canal, the normal gates w ould just drift open, but the additional pair of
gates can be closed to protect the canal, and prevent navigation to the river. In effect, we have simply added a flood gate.
 As above, but where it is safe to navigate even when the river is higher than the canal. The lock w illbe fully bidirectional (tw o pairs of oppositely pointing gates at each end) to
allow boats to pass at any normal river levels. At extreme low or high tides unsuitable for navigation, the appropriate sets of gates are barred to prevent passage.
Inlet Locks
Inlet lock (left) fromfeeder canal, regulates w aterfromthe Potomac river into the C&O canal. Lift lock (right) allow s boats to continue up the canalin a normal fashion.
An inlet lock is to regulate w ater froma feeder canalor a river into the main canal. In some cases, the inlet lock may double as a lift lock to allow boats into the river slackw ater. Note
that in the example on the right, the feeder canalw as originally George Washington's Little Falls Skirting Canal w hich waspart of the Potomac Company's canals, later re-purposed as
a feeder canalfor the Chesapeake and Ohio Canal.
Very large locks
Berendrecht Lock(right) and Zandvliet Lock (left), located at the entrance to the Port of Antw erp (top) fromthe Scheldt (foreground)

21. Barges at a lockon the Mississippi River
The w orld's largest lockw as, until2016, the Berendrecht Lock, giving access to the Port of Antwerp in Belgium. In 2016 the Kieldrechtsluis in the same port became the largest. The
lock is 500 m (1,600 ft) long, and 68 m (223 ft) w ide and drops 17.8 m (58 ft), and has four sliding lockgates. The size of locks cannot be compared w ithout considering the difference
in w ater levelthat they are designed to operate under. For example, the Bollène lock on the River Rhône has a fallof at least 23 m (75 ft), the Leerstetten, Eckersmühlen and
Hilpoltstein locks on the Rhine–Main–Danube Canal have a fall of 24.67 m (80.9 ft), each and the Oskemen Lock on the Irtysh River in Kazakhstan has a drop of 42 m (138 ft).[33]
The
total volume of w aterto be considered in any lock equals the product of its length, breadth and the difference in w ater levels. Lockstaircases are used in an attempt to reduce the total
volume of w ater required in relation to the amount of usefulw orkdone. The usefulw orkdone relates to the w eight of the vesseland the height it is lifted. When a vesselis low ered the
consumption of potential energy of the w ater consumed is considered. An alternative to locks is a boat lift; facilities of this type, e.g. the Anderton boat lift or the Strépy-Thieu boat lift in
Belgium, do not rely on the consumption of w ater as the primary pow er source, are powered by motors and are designed to consume a minimum amount of w ater.
The 29 locks on the Mississippi River are typically 600 feet (180 m) long w hile tug and barge combinations are as much as 1,200 feet (370 m) long consisting of as many as 15 barges
and one tug. In these cases, some of the barges are locked through, using partially opened lock valves to create a current to pull the un-pow ered bargesout of the lockw here they are
tied up to w ait for the rest of the barges and the tug to pass through the lock. It can take as much as an hour and a half to pass the lock.
The gates of a Guillotine lock w orkin a w ay similar to a sluice gate, but most canallock gates are hinged to sw ing like doors.
Hiram M. Chittenden Locks
Every November, the large lock of the Hiram M. Chittenden Locks (better know n locally as the "Ballard Locks" in reference to the Seattle neighborhood they are located in) w as
emptied for maintenance, as seen in the November 2004 pictures below . This provides an opportunity to visualize how a lockw orks without the waterobscuring the bottom of the lock.
For reference, the picture far left shows the lockin operation, w ith a tug and a barge (loaded w ith sand and gravel) w aiting for the gates to open. In the bottom left corner of the picture
may be seen the cut-out in the side w allthat contains the gate w hen open.
The lock has three pairs of gates, one pair at each end and one pair in the middle so that half the length of the lock can be used w hen the w hole length is not required, thus saving
w ater. The barely visible person w alking along the bottom of the lock in the second picture gives an indication of the vast size of this lock. In both pictures of the end gates, the string
of penstockopenings are visible along the sides at the bottom. The w ater entering and leaving the lock flow sby gravity through these openings. It requires around 15 minutes to fill or
empty the lock.

22. 
Hiram M. Chittenden Locks: tug and barge in lock w hen full.

Lock emptied for maintenance – low w ater end of the lock.

Lock emptied for maintenance – centre pair of gates.

Lock emptied for maintenance – high w ater end of the lock.
Van gate

23. A van gate
1: Tube connecting the chamber to the high w ater side of the sluice
2: Gates to regulate the w ater levelin the chamber
3: Tube connecting the chamber to the low water side of the sluice
4: The chamber in w hich the w aterlevelcan be controlled
5 Door w ith larger surface
6: Door w ith smaller surface.
This type of gate w as a Dutch invention in the early 19th century. The Van gate has the specialproperty that it can open in the direction of high w atersolely using w aterpressure. This
gate type w as primarily used to purposely flood certain regions, for instance in the case of the Hollandic Water Line. Now adays this type of gate can stillbe found in a few places, for
example in Gouda.
The design of a Van gate is show n in the image on the low er right. When the tube connecting the separate chamber w ith the high w ater levelside of the sluice is closed and the
connection w ith the low waterlevelside opened, the w ater levelin the separate chamber w illdrop to the level on the low water levelside of the sluice. The surface area of the gate
separating the chamber fromthe high w ater levelside of the sluice is larger than that of the gate closing the sluice. This results into a net force that opens up the sluice.
History and development[edit]
Dams and weirs

24. In ancient times river transport wascommon, but rivers w ere often too shallow to carry anything but the smallest boats. Ancient people discovered that rivers could be made to carry
larger boats by making dams to raise the w ater level. The w ater behind the dam deepened until it spilled over the top creating a w eir. The w ater wasthen deep enough to carry larger
boats. This dam building w as repeated along the river, until there w ere "steps" of deep water.
Flash locks
The development of dams and w eirs created the problemof how to get the boats betw een these "steps" of water. An early and crude way of doing this w as by a flash lock. A flash lock
consisted essentially of a small opening in the dam, w hich could be quickly opened and closed. On the Thames in England, this w as closed with verticalposts (known as rymers)
against w hich boards were placed to blockthe gap.
When the gap w as opened, a torrent of w ater would spillout, carrying a "dow nstream" boat w ith it, or allow ing an "upstream" boat to be man hauled or w inched through against the
flow . When the boat w as through, the opening w ould be quickly closed again. The "gate" could also be opened to release a 'flash' dow nstreamto enable grounded boats to get off
shoals, hence the name.
This systemw as used extensively in Ancient China and in many other parts of the w orld. But this method w as dangerous, and many boats w ere sunkby the torrent of w ater. Since this
systemnecessarily involved lowering the levelin the pound, it w as not popular w ith millers w ho depended on a full head of w ater to operate their equipment. This led to constant
battles, both legal and physical, betw een the navigation and milling interests, w ith riversbeing closed to navigation if there w as any shortageof water. It w as mainly this conflict, w hich
led to the adoption of the pound lock in medieval China, as this means that relatively little w ater is consumed by navigation.
Staunch
A more sophisticated device w asthe staunch or w atergate, consisting of a gate (or pair of mitred gates) w hich could be closed and held shut by w ater pressure when the river was
low , to float vessels over upstreamshallows at times of low water. However, the whole upstreamhead of w ater had to be drained (by some auxiliary method approaching modern
sluices) before a boat could pass. Accordingly, they were not used w here the obstacle to be passed w as a mill w eir.
Pound lock
Model of early river pound lock, constructed in Lankheet w ater park, Netherlands
The natural extension of the staunch w as to provide an upper gate (or pair of gates) to form an intermediate "pound" w hich was allthat need be emptied w hen a boat passed through.
This type of lock, called a pound lock w as known in Imperial China and Europe.[34]
Pound locks w ere first used in medieval China during the Song Dynasty (960–1279 AD).The Songshior History of the Song Dynasty, volume 307, biography 66, records how Qiao
Weiyue, a high-ranking tax administrator, w as frustrated at the frequent losses incurredwhen his grain barges w ere wrecked on the West River near Huai'an in Jiangsu. The soldiers
at one double slipw ay, he discovered, had plotted w ith bandits to w reckheavy imperial barges so that they could stealthe spilled grain. In 984 Qiao installed a pair of sluice-gates tw o
hundred and fifty feet apart, the entire structure roofed overlike a building. By siting tw o staunch gates so close by one another, Qiao had created a short stretch of canal, effectivelya
pound-lock, filled fromthe canal above by raising individual w ooden baulks in the top gate and emptied into the canal below by low ering baulks in the top gate and raising ones in the
low er.[3]

25. The turf-sided Monkey Marsh Lockon the Kennet & Avon Canal at Thatcham
Turf-sidedlock
A turf-sided lockis an early formof canal lock design that uses earth banks to formthe lock chamber, subsequently attracting grasses and other vegetation, instead of the now more
familiar and w idespread brick, stone, or concrete lockwallconstructions. This early lockdesign w as most often used on river navigations in the early 18th century before the advent of
canals in Britain. The sides of the turf-lockare sloping so, w hen full, the lock is quite w ide. Consequently, this type of lock needs more w ater to operate than vertical-sided brick- or
stone-walled locks. On British canals and w aterwaysmost turf-sided locks have been subsequently rebuilt in brickor stone, and so only a few good examples survive, such as
at Garston Lock, and Monkey Marsh Lock, on the Kennet and Avon Canal.[35]
Use of water
The main problem caused by locks is that, each time a lock goes through one fill–empty cycle, a lockful of w ater (tensof thousands up to millions of litres) is released to the low er
pound. In more simplistic terms, on a canal w here only one boat w illfit into a lock, a boat travelling from the summit pound to the low est pound is accompanied on its journey by one
'personal' lockfulof w ater. A boat going the other w ay also transfersa lockfulof w aterfromthe summit pound to the low est pound. To prevent the canal fromrunning dry, some method
must be used to ensure that the w ater supply at the canalsummit is constantly replenished at the rate that the w ater is being drained dow nwards. This is, of course much more of a
problem on an artificialcanal crossing a w atershed than on a river navigation.
Design[
When planning a canal, the designer w illattempt to build a summit level w ith a large reservoir, or one supplied by an artificialw atercourse froma distant source, or one as long as
possible (to act as its ow n reservoir) or which cutsacrossas many springs or rivers as possible (or allof these). Driving the summit level through a deep cutting or tunnel may cut
through the w ater table as w ellas underground sources of water.
Pumping
Where it is clear that natural supply w illnot be sufficient to replenish the summit level at the rate that w ater willbe used (or to allow for unexpectedperiods of drought) the designer
may plan for w ater to be back-pumped back up to the summit from low er down. Such remedies may of course be installed later, w hen poor planning becomes apparent, or w hen there
is an unforeseeable increasein traffic or dearth of rain. On a smaller scale, some local pumping may be required at particular points (w ater is continually recycled through some locks
on the Kennet and Avon canal).
Water savingbasins

26. Disused side pond at Atherstone on the Coventry Canal, England
A w ay of reducing the water used by a lockis to give it one or multiple reservoirs, whose levels are intermediate betw een the upper and low er pounds. These reservoirs can store the
w ater drained fromthe lock as a boat descends, and release it to fill the next time a boat ascends. This saves half the amount of w ater lost downhillin each fill–empty cycle. Generally
these reservoirs are called "saving basins".
Installing a single side pond w illsave 1/3 of the w ater, whereasthree side ponds w illsave 60% of the w ater: the first 1/5 of the w ater goes into the top pond, the 2nd 1/5 into the middle
pond, the 3rd 1/5 into the bottom pond – and 2/5 is w asted at each passage (assuming the area of each pond equals the area of the lock). The formula for side ponds of
optimal altitude and depth, w ith area of each pond, , and area of the lock, , is:
.[36][better source needed]
Diagram of w ater saving basins (descending)
Diagram of w ater saving basins (ascending)

27. For example, the Hindenburg-lock (in Hannover, Germany, built 1919–1928) has tw o lockchambers of 225 m length, each of w hich would use 42,000 m³ of w ater fora fulllocking
cycle. Due to the use of 10 w ater saving basins, only 10,500 m³ of w aterare used. A more recent example is the Rhine–Main–Danube Canal w ith 13 saving locks out of a total of 16
locks.
Water saving basins are incorporated in proposals to augment the capacity of the Panama Canal, but the scheme is controversialbecause the mixing of salt and fresh waterin the
basins w illallow brackish water into Gatun Lake, a source of drinking w ater and a w ildlife reserve.[37][38]
Map show ing extended intermediate pounds at Caen Hill locks
On English canals, these reservoirs are called "side ponds". The Droitw ich Canal, reopened in 2011, has a flight of three locks at Hanbury w hich allhave operational side
ponds.[39]
Side ponds w ere also installed on the Grand Union Canal and the Coventry Canal, among others. They are now out of use, and in some cases have been filled in, because
British Waterw aysconsidered that it w as too easy to misuse them and flood the surrounding area.[citation needed]
On some flights of locks w ith short intermediate pounds, the pounds are
extended sidew ays – in effect to provide a reservoir to ensure that the pound does not run dry (in case, for instance, the lockbelow leaks more than the lock above). These extended
intermediate pounds are sometimes confused with side ponds.
Alternatives[
As w ellas the "static" approaches mentioned earlier (various types of contouring, excavating, and spanning), there w ere many ingenious "dynamic" solutions, mostly variations on the
boat lift or the inclined plane. These tend to be more expensive to install and operate, but offer faster transit and waste less water.
Inclined plane
Boat in cradle, at the top of inclined plane on the Morris Canal.
An inclined plane consists of a cradle (to hold a barge) or caisson (a box full of w ater in w hich a barge can float) w hich moves on rails sidew aysup a slope fromone w aterwayto the
other. Since the box is "w et" (filled w ith water), Archimedes' principle ensures that the caisson alwaysweighsthe same, regardless of the size of boat being carried (or even if it
contains only w ater). This makes for easy counterbalancing by a fixed w eight or by a second caisson. The motive pow er may be steam or hydraulic, or may come from overbalancing
the top caisson with extra waterfromthe upper w aterway.

28. There are no w orking w aterwayinclined planes in the UK at the moment, but the remains of a famous one can be seen at Foxton in Leicestershire on the Leicester arm of the Grand
Union Canal. The plane enabled w ide-beamboats to bypass the flight of ten narrow locks, but failure to make improvements at the other end of the arm and high running costs led to
its early demise.[40]
There are plans to restore it, and some funding has been obtained.[41]
Marine railway
Big Chute Marine Railw ay in the Trent-Severn Waterway, Ontario, Canada
A marine railw ay is similar to a canal inclined plane in that it moves boats up or dow n a slope on rails. How ever, the vesselis carried in a dry carrying frame, or cradle, rather than in a
w ater-filled caisson. The principle is based on the patent slip, used for hauling vessels out of the w ater formaintenance.
In operation, a boat is navigated into the carrying frame, w hich has been low eredinto the w ater. The boat is secured to the cradle, possibly by raising slings under the hull
using hydraulics, and the cradle is hauled out of the w ater and up the hill w ith a cable. At the top of the slope, the cradle is low ered into the upper w aterway,and the boat released. As
the boat is not floating, Archimedes' principle does not apply, so the w eight lifted or low ered by the device varies – making counterbalancing (by dead w eights or a second boat
carriage) more difficult.
In some locations, such as the Big Chute Marine Railw ay on the Trent-Severn Waterway, in Ontario, Canada, a marine railw ay was installed as a temporary measure at the planned
site of a flight of conventionallocks. In this and severalother cases, the locks w ere neverbuilt, and the marine railw ay continued to serve on a permanent basis.
Boat lift
The Falkirk Wheel, the w orld's first rotating boat lift, acts as the centrepiece of the restoration of the Forth and Clyde and Union Canals. The Wheel replaced a flight of locks w hich
formerly connected the canals and w hich werefilled in in 1930. It w as the w inning design in a competition to design a new lock. Visitors can now take a boat trip on the Wheel and be
lifted over 100 feet (30 m) in a few minutes compared to the time it took w hen the original lock staircase operated.[clarification needed]
The Victorian Anderton Boat Lift, the w orld's first verticalboat lift, linking the Trent and Mersey Canal and the River Weaver in Cheshire, has recently[when?]
been restored. The w orld's
highest boat lift in Strépy-Thieu in Belgium raises or low ers 1,350 tonnes boats by 73.15 metres.
Another derivative is the Peterborough lift lock w hich is a boat lift located on the Trent Canal in the city of Peterborough, Ontario, Canada and is Lock21 on the Trent-Severn
Waterw ay. Its dual lifts are the highest hydraulic boat lifts in the w orld, rising 19.8 m (65 ft). This w as a considerable accomplishment w hen conventionallocks usually only had a 2 m
(6.6 ft) rise. Each lift has a capacity of 1,300 tonnes. The basins are 140 feet (43 m) long, 33 feet (10 m) w ide and 9 feet 10 inches (3.00 m) deep. The verticaldistance lifted is 65 feet
(20 m). The Trent-Severn has another similar lift lock at Kirkfield, w ith basins of the same dimension, but w hich lifts over a smaller verticaldistance.
Caisson lock

29. Operation of caisson lock
Around 1800 the use of caisson locks w asproposed by Robert Weldon for the Somerset Coal Canal in England. In this underw ater lift, the chamber w as80 ft long and 60 ft (18 m)
deep and contained a completely enclosed w ooden box big enough to take a barge. This box moved up and dow n in the 60 ft (18 m) deep pool of w ater. Apart frominevitable leakage,
the w ater never left the chamber, and using the lock w asted no water. Instead, the boat entered the box and w as sealed in by the door closing behind it, and the box itself w as moved
up or dow n through the w ater. When the box w as at the bottom of the chamber, it w as under almost 60 feet (18 m) of w ater – at a pressure of three atmospheres, in total. One of these
"locks" w as built and demonstrated to the Prince Regent (later George IV), but it had various engineering problems and the design w as not put into use on the Coal Canal.[42][43]
Hydro-pneumatic canal lift
Possibly inspired by Weldon's caisson lock, William Congreve in 1813 patented a "hydro-pneumatic double balance lock" in w hich two adjacent locks containing pneumatic
caissons could be raised and low ered in counterbalance by the movement of compressed air fromone caisson to the other. In about 1817 the Regents Canal Company built one of

30. these locks at the site of the present-day Camden Lock, north London. Here the motivation w as, again, water supply problems. The company insisted on various modifications to
Congreve's design; the resulting installation proved to be unsatisfactory, and wassoon replaced by conventionallocks.[44][45]
Shaft lock
Entrance to Minden shaft lock
Looking superficially similar to the caisson lockis the shaft lock. Shaft locks consist of a deep shaft w ith conventionalupper gates. The low er gates are reached through a short tunnel.
The gates only close off this approach tunnelso do not have to reach the full height of the lock. Notable examples have been built at Saint Denis (Paris, France), Horin (near Melnik,
Czech Republic) and Anderten (Hannover Germany).[46]
The shaft lockat Minden 52°18′23″N 8°55′11″E has a fall of 12.7 metres (42 ft) and has eight tanks linked in pairs to the lock
chamber.[47]
As the lock is emptied w ater is run into each chamber in turn, for filling the w ater is released f romthe chambers thus saving the w asteof a complete lockfull of w ater. An
earlier attempt at a shaft lockhad been made at Trollhättan in Sw eden on the line of the present Göta canal. The fallw ould have been 16 metres (52 ft), astonishing in 1749. How ever
the approach tunnelproved to be unusable in times of flood and the shaft lockw as replaced by a 2-rise staircase in 1768.[48]
Diagonal lock
This new concept in lock design has yet to be installed on any w aterway. It is basically a shaft lockw ith a diagonal shaft. The proposalis for a long tube of reinforced concrete, of a
size to accommodate the boats being lifted, to be built on the slope betw een the upper and low er levels. The bottom of the tube is sealed w ith a strong w atertight door, but there is a
single pair of conventionallockgates at the top, installed a boat's length fromthe far w allof the tube. The change in level is achieved by filling the tube w ith water fromthe top pound,
or by draining. The vesselfloats on the surface of the w ater, with a guide float or pontoon, shaped to fit the tube, floating alongside to keep it clear of the w alls. Side ponds, piped from
the main tube, are incorporated to save w ater. In replacing a traditional flight or staircase of locks, a considerable time saving is anticipated. It differs fromthe similar caisson
lock design in that the boat does not have to be carried in a submerged chamber.
The "Diagonal Lock Advisory Group" has identified severalsites in Britain w here the new design could be installed, either on new w aterwaysor canals under restoration.[49]
Projects
under consideration include the restoration of the Lancaster Canal to Kendal and the proposed new branch of the Grand Union Canal betw een Bedford and Milton Keynes.
Three Gorges Dam model view . A pair of five locking steps is at center w ith a ship lift to the left
A combinedsystem – the Three Gorges Dam

31. At the Three Gorges Dam on the Yangtze River (Chang Jiang) in China there are tw o stairsteps of five large ship locks (each 300 m long and 35 m w ide) for ten-thousand-tonne ships.
In addition to this there w illbe a boat lift (a large elevator) capable of moving a three-thousand-ton ship vertically in one motion. The locks and the boat lift provide a total lift of up to
113 metres.
Ship sizesnamed after locks
Locks restrict the maximum size of ship able to navigate a w aterway, and some key canals have given rise to the name of standard ship sizes, such as the Panamax and
the Seaw aymax.
MY COMMENTS:--
It's a news clip published in the Times of India,28th June,2018 ,Kolkata edition ,in thebusiness section.A dangerous non technical move is being taken to put thedock complex in
danger.The tide level at Haldia lock is +0.1 to +7.7m,from lowest tide to the HHWL.The design of civil structures and mechanical handling equipments had been finalised and
installed based on this tidal conditions,waves and wind rose.This is likely to have a dangerous blunder on the operation of the dock systemand thevessels parked there in the dock
basin.The working level of the jetties and wharves have been fixed at +4.5m from chart datum.So,the founding level of piles and monoliths have been fixed accordingly.If thelock
gates remain open for tidal variations for experiment,the experiment may be a very costly experiment.If the tide falls,the vessels berthed inside may go aground and will be a
difficult task,if not impossible,to get thevessels afloat.The depth increase by dredging is also having limitations as it is likely to expose the footings of the supporting
structures,making them weaker to fall down.Thereach of the handling equipments inside thevessels bottomcargo will not be p ossible at LLWL.Moreover,during rising and falling
tides,thegates cannot be operated and closed due to inherent design of the gates and thehydrodynamics and hydrostaticforces thereof.In my opinion,IIT,CHENNAI,arenot the
right experts for such dangerous and ornamentally costly experiments.I refer to their credentials of berth 11 and 12 of Kandla port trust,wheretheberths inclined towards sea due to
bad proof check of designs and construction methodology.They have no practical experience of a port design on such a tidak river.IIT,KGP,did some model tests of haldia dock as
far as it can be recollected.However,such a move should only be taken after deep thought and judicious approach not to close down the haldia dock once for all.This is posted for
noting and suitableaction by theGOI,MINISTRYOF SHIPPING,Chairman.KoPT.